1. Field of Invention
The present invention relates to an improved method for photoresist residue. More particularly, the present invention relates to an improved method for photoresist residue on a surface of a titanium nitride layer.
2. Description of Related Art
In semiconductor processes, a patterned method uses photoresist material to transfer patterns. Photoresist material is sensitive to light. Through exposure and development, a photoresist layer is formed to serve as an etching mask. With the photoresist layer serving as a mask, the underlayer is patterned.
Etching different material needs a suitable photoresist material serving as an etching mask. However, while etching titanium nitride, the photoresist material serving as a mask for etching the insulating layer causes damage to the titanium nitride. In a conventional method, a photoresist layer is directly formed on the titanium nitride. This causes a defect on the surface of the titanium nitride bottom electrode, and a portion of the photoresist material may remain on the surface of the bottom electrode.
A semiconductor process for a fingerprint sensor is taken as an example. After an interconnect is fabricated, a sensor region having an area of about 2.25 cm.sup.2 which is like a finger is formed over a top surface of a semiconductor substrate. The layout of the sensor region has a capacitor with about 300 lines and about 300 rows. Titanium nitride is commonly used for a material for a bottom electrode of the capacitor. The fingers serve as an upper electrode of the capacitor. The capacitor in the fingerprint sensor is used to induce static electricity on a fingertip surface. The fingertip surface is composed of raised lines and depressions between the raised lines. The capacitance induced by the raised lines is different from that induced by the depressions, and this difference is read by the sensor. Finally, the signals are transformed into an image.
In fabrication of a conventional fingerprint sensor, after an interconnect is fabricated, a patterned titanium nitride layer is deposited to serve as a bottom electrode. Then an opening is formed in a silicon oxide layer between a pad and a titanium nitride layer to serve as a connection in a latter package process. While patterning the silicon oxide layer, a photoresist layer is formed on the silicon oxide layer and the titanium nitride layer. However, the titanium nitride layer is damaged by the photoresist material to cause a defect generated on a surface of the titanium nitride layer. Moreover, some photoresist residue remains on the surface of the titanium nitride layer. As a result, the quality of the capacitor is thus decreased.